Overo Lethal White Syndrome: What Is It?

Overo Lethal White Syndrome, or OLWS, is a syndrome seen in overo paint horses when the foal is born completely white. This syndrome is a genetic condition that causes guaranteed death in the baby horses who are born with it. What causes this mysterious condition? And how is it fatal? This is all about Overo Lethal White Syndrome.

What Is Overo Lethal White Syndrome?

Overo Lethal White Syndrome is a condition seen in Overo Paint Horses which causes a foal to be born completely white with a number of health issues that lead to guaranteed death. This condition is an issue that is caused genetically. It is mainly frame overo horses that have offspring suffering from OLWS. Foals born with this condition mainly will die from an underdeveloped digestional tract.

What Are The Symptoms Of OLWS?

There are many different symptoms of Overo Lethal White Syndrome. Some of these symptoms include:

White Coat

Like the name might suggest, foals born with OLWS have a completely white coat without any dark markings or pigmentation in their coat. These foals are often mistaken for true white or albino horses because in appearance they carry many of the traits of an albino or true white horse.

Pink Skin

Foals with OLWS not only have a white coat, but they also have pink skin. This trait as well makes some wonder if a horse is albino or not. Pink skin in these foals is a trait also seen in albino and true white horses which is why these horses are mistaken for albino horses sometimes.

Pale Blue Eyes

Like many other horses who have color dilution, the eyes of these horses is usually pale blue in color. They may also be:

  • Pink
  • White
  • Pale Green
  • Pale Yellow


Sadly, because of their condition, Lethal White foals often suffer from deafness. This is caused from poor development and sensitivity to a variety of things due to the lack of their pigmentation and other issues that these horses might have.

Colic Symptoms

Because these foals suffer mainly from an underdeveloped digestive tract, they often suffer from extremely painful colic symptoms. These symptoms are caused by gas and manure not being able to pass through a horse’s digestive tract or intestines due to the deformities that have internally on this part of the horse’s body.

Not only will these horses suffer from extreme colic symptoms, but they also suffer from other things (listed below)

What Causes OLWS?

OLWS is a genetic condition that is caused by the breeding of two horses that carry this defective gene. The most common coat color or pattern to carry this gene and give birth to lethal white foals is the overo coat color, especially frame overo horses.

Is OLWS Preventable?

Yes, the best way to prevent OLWS is to breed your horse, especially if it is a carrier of the lethal white defective gene, to a horse that is completely clear of this gene. You want to stay away from carrier horses because it will lower the possibility of you having a lethal white foal and it will also lower the number of lethal white foals being born.

What Are The Different Names & Abbreviations Of Overo Lethal White Syndrome?

There are so many different names and abbreviations for this condition. The following names and abbreviations when seen in the horse world mean that that horse has Overo Lethal White Syndrome:

  • OLWS
  • Overo Lethal White Syndrome
  • LWS
  • Lethal White Syndrome
  • Lethal White
  • Overo Lethal White Foal Syndrome
  • LWO
  • Lethal White Overo
  • LWOS
  • Lethal White Overo Syndrome

Can You Tell If A Horse Is A Carrier For OLWS?

Yes. One way to tell if your horse is a carrier of OLWS is by looking at the foals that they have had and determining of any of them are Lethal White foals. If any of them are, your horse is most likely a carrier.

Another way to tell if your horse is a carrier is by getting genetic testing done on your horse. If your horse is a carrier, the genetic testing will show this. One way to do genetic testing is by bringing a hair sample to a veterinary laboratory to determine if your horse carries this gene.

How Long Does A Foal With OLWS Last?

If a foal is born with the lethal white syndrome, it is most likely that it won’t last more than a week. In most cases, these foals are humanely put down because if they aren’t they will die a slow, painful, and miserable death.

Can A Horse Survive OLWS?

Sadly there are no survivors of OLWS. This is because of the variety of complications that these foals have. The different defects and illnesses that these horses suffer from include:

  • Defective Digestive Tract
  • Colic
  • Poisoning From Their Own Waste
  • Trouble Passing Manure
  • Abdominal Pain
  • Rolling
  • Thrashing
  • Rapid Breathing & Hyperventilation
  • Excessive Sweating
  • Distended Belly

Fun Facts On OLWS

  • Foals with OLWS are usually put to sleep because of their hopeless condition
  • The gene that causes Overo Lethal White Syndrome is comparable to that of the creme gene where it affects the horse’s coat color. While two copies of the creme gene in a chestnut horse would cause a cremello coat color, two copies of this defective overo gene cause Overo Lethal White Foal Syndrome

Hailey Sipila

Horses have been my passion ever since I can remember. At school, I was known as that weird horse girl, and I would read horse encyclopedias for fun. Over the years since those days, I have only learned more. My experiences with horses of a variety of breeds have taught me a lot. Now I want to share what I know with you!

Recent Posts